The first day of June 1967 saw the release of an album that would provide the soundtrack for the approaching summer. For weeks to come, nearly everywhere you went, you would hear it: on the radio, in restaurants and clubs, from passing automobiles and through the open windows of homes, where it spun repeatedly on turntables.

Sgt. Pepper’s Lonely Hearts Club Band was the album, and it was the Beatles’ latest and greatest achievement. The record defined not only that summer—dubbed the Summer of Love—but also the year and, eventually, the moment at which pop music became art. Until then, pop music had been written and produced for teenagers, and teenage music was not supposed to be like this: sophisticated, challenging, as carefully wrought as an objet d’art.

With Sgt. Pepper’s, the Beatles redefined the genre even further than they had the previous year with Revolver, creating grand productions punctuated by calliopes, classical Indian instruments, orchestras, animal noises, sound effects and layered crashes of piano chords. Pressed onto a 12-inch slab of vinyl and packed into a baroque, parti-colored sleeve, the music on Sgt. Pepper’s constituted not just an album but an event—a pivotal moment in the development of Western music.

So what do you do for an encore? Seizing the moment, the Beatles might have carried onward with a music project even grander, or defied expectations and taken a completely different artistic direction. In fact, they would do both in 1968 with their sprawling, stripped-down double-disc White Album.

But in the meantime, in late April 1967, with the Sgt. Pepper’s sessions barely finished and the album still unreleased, they launched haphazardly into a new project based on, of all things, an art-film concept dreamed up by their bassist, Paul McCartney. Titled Magical Mystery Tour, it was designed from the beginning as a TV film that would include the Beatles both as actors and as musical performers. The idea had come to McCartney on April 11 during a return flight from the U.S. to Britain.

The Beatles had quit touring the previous August, and a film, he reasoned, would be a good way to keep them in the public eye. In fact, it would be little more than a container for six new Beatles songs: the title track, “Your Mother Should Know,” “The Fool on the Hill,” “Blue Jay Way,” “I Am the Walrus” and “Flying.” Accordingly, the film’s plot was slight and functional: a bus carrying the band and a group of tourists through provincial England comes under the power of a cadre of magicians (also played by the Beatles), after which strange things start to happen. As a story device, the bus tour was certain to appeal to British viewers.

“It was basically a sharabang trip,” George Harrison said, “which people used to go on from Liverpool to see the Blackpool Lights,” a popular electric light display presented in the autumn months. “They’d get loads of crates of beer and an accordion player and all get pissed, basically—pissed in the English sense, meaning drunk. And it was kind of like that. It was a very flimsy kind of thing.”

As John Lennon saw it, “It’s about a group of common, or ‘garden,’ people on a coach tour around everywhere, really, and things happen to them.”

No one in the group took the concept very seriously. The Beatles didn’t hire big-name screenwriters or a visionary director, or pour loads of money into the production. They simply signed up some character actors—including Jessie Robins as Ringo Starr’s bellicose, fat aunt, and eccentric Scottish poet and musician Ivor Cutler as the skeletal Buster Bloodvessel—hired out a coach, and hit the English countryside, filming a series of bizarre and droll sketches designed to support the title’s dual notions of magic and mystery.

“We rented a bus and off we went,” Starr says. “There was some planning. John would always want a midget or two around, and we had to get an aircraft hangar to put the set in. We’d do the music, of course. They were the finest videos, and it was a lot of fun.”

Indeed, the entire last half of 1967 was a strange time for the Beatles. Concurrent with the start of Magical Mystery Tour, they’d agreed to provide music for Yellow Submarine, an animated film based on their 1966 song of the same name from Revolver. Film productions had been a secondary aspect of the Beatles’ career ever since their 1964 feature film debut, A Hard Day’s Night. Now, however, they were involved in two films simultaneously. In addition, at nearly the same time that they’d agreed to Yellow Submarine, their manager, Brian Epstein, had signed them up to appear on Our World, a live global television event scheduled for June 25, for which the Beatles would compose and perform a new composition, “All You Need Is Love.”

Clearly, there was no shortage of projects for the group to work on. The problem was that, after an intense five months of recording Sgt. Pepper’s, they found it difficult to focus again on a new project, let alone three.

“I would say they had no focus, absolutely,” says Ken Scott, the Abbey Road engineer who ran the mixing console for several of Magical Mystery Tour’s songs. (His recollections of working with the Beatles as well as recording classic albums by David Bowie, Elton John, Supertramp and others are chronicled in his new memoir, Abbey Road to Ziggy Stardust.) “It was kind of weird, ’cause I’d worked with them from A Hard Day’s Night through Rubber Soul as a second engineer, and I’d seen sort of how they would get down to work and all of that kind of thing. But on Magical Mystery Tour, the focus didn’t seem there. It was kind of thrown together.”

A survey of the group’s recording sessions from this period bears out his point. Between the completion of Sgt. Pepper’s on April 21 and the conclusion of sessions for Magical Mystery Tour the following November, the group recorded about an album’s worth of songs, several of which remained unmixed or unfinished for another year, some for even longer. In addition to the six Magical Mystery Tour tracks, the Beatles recorded McCartney’s “All Together Now,” and Harrison’s “Only a Northern Song” and “It’s All Too Much,” all of which ended up on the Yellow Submarine soundtrack, released in January 1969. Also started during this time was the recording of Lennon’s novelty tune “You Know My Name (Look Up the Number),” which remained unfinished until late 1969 and unreleased until 1970.

Which is not to imply that the Beatles lacked motivation. Geoff Emerick, who engineered Revolver, Sgt. Pepper’s and much of Magical Mystery Tour, believes their almost nonstop working schedule from 1962 through 1967 had everything to do with their lack of direction in the wake of Sgt. Pepper’s. In his 2006 memoir, Here, There and Everywhere, he recalls, “People don’t realize how hard the Beatles worked in the studio, and on the road. Not just physically, but psychologically and mentally it had to have been incredibly wearying. Now”—with the completion of Sgt. Pepper’s—“it was time to let off some steam. All throughout the spring and summer of 1967, the prevalent feeling in the group seemed to be: after all those years of hard work, now it’s time to play.

“Personally, I saw it as just a bit of harmless light relief after all the intensity that had gone in to Pepper. The question was, how long could it last before they got bored?”